The invention relates to a method for interrupting the regeneration of a particulate filter in the exhaust gas system of a diesel engine, with the mass air flow rate (MAF) and the intake manifold absolute pressure (MAP) being detected by sensors. More particularly, the invention relates to closed-loop control for interrupting the regeneration of a diesel particulate filter (DPF), when the temperature in the DPF is too high, by controlling an intake throttle valve and an exhaust gas recirculation (EGR) valve.
Soot particles are removed from the exhaust gas flow from a diesel engine by arranging one or more diesel particulate filters (DPF) in the engine""s exhaust system. Since particulate matter accumulates during operation, particulate matter is removed from the filter when the filter load exceeds a predetermined threshold. A regeneration or oxidation process, which is carried out onboard the vehicle, is the preferred approach for this purpose in automobiles. Regeneration of the DPF is carried out by increasing exhaust gas temperature to allow combustion of accumulated particulate matter in the presence of adequate oxygen.
During regeneration, DPF temperature must be kept below a critical threshold to prevent thermal damage to the DPF. If the threshold is exceeded, measures can be taken to interrupt regeneration as quickly as possible. An uncontrolled combustion rate in a DPF can cause it to melt. Such a situation can occur, for example, by the air supply being excessively restricted for a relatively long period followed by unrestricted operation. In this situation, the rise in the oxygen supply initiates an excessive combustion rate in the overheated DPF.
Patent Abstract JP 60090931 describes using an intake throttle valve to limit the supply of fresh air if a filter temperature above a predetermined limit is detected.
According to Patent Abstract JP 01087820, an oxygen sensor is provided, which is arranged on the inlet side of the DPF and is intended to control the combustion rate of the particulate matter, and hence the temperature rise in the filter, by restricting intake air flow by adjusting the intake throttle valve.
According to Patent Abstracts JP 05133285 and JP 05106518, an intake throttle valve and an EGR valve are used to control DPF regeneration. During regeneration, EGR is reduced in relation to time without regeneration. If deceleration occurs during the regeneration process, the EGR valve is completely opened, while the fresh air is restricted. This further reduces the oxygen content in the exhaust gas flow.
The inventors of the present invention have recognized a twofold method for interrupting regeneration. First, measures that have been taken to increase the exhaust gas temperature in the inlet to the DPF are discontinued. Secondly, the oxygen concentration in the exhaust gas flow to the DPF is reduced as suddenly as possible. The amount by which the oxygen concentration is limited is governed by the stability of the combustion process in the engine, so that correct engine operation is maintained.
The first type of measures include: switching off auxiliary loads, (such as electrical loads, eg., glow plugs or increased idle speed), measures which reduce combustion efficiency (eg., retarding injection timing, lowering pressure of injection), measures to transfer heat into the intake stream, the exhaust stream, or both (eg., external heaters, post injection of fuel late in the expansion stroke, injection of fuel into the exhaust stream using an additional injector located in the exhaust duct), measures to stimulate an exotherm in an oxidation catalyst placed in front of the DPF (eg., increasing amount of unburned fuel in the exhaust stream).
The second measure can be achieved by actuating the intake throttle valve and the EGR valve. During forced regeneration of the DPF: the EGR valve is typically fully closed to maximize oxygen concentration in the exhaust gas; and the intake throttle valve would be closed to increase pumping load on the engine and to reduce flow rate through the engine, which increases engine out temperature. The inventors of the present invention have recognized that it is preferable to coordinate the positions of the EGR and intake throttle valves during forced regeneration so that a desired oxygen concentration at the inlet to the DPF exists. To halt the regeneration process, the air-fuel ratio is reduced as much as possible without causing engine stability to degrade beyond an acceptable level. Preferably, this is accomplished by opening the EGR valve to a maximum position and closing the intake throttle as little as necessary to achieve maximum flow rate of the products of stoichiometric combustion through the DPF. This control action is carefully coordinated to avoid flushing the highly heated filter material with an oxygen-rich exhaust.
Disadvantages of prior approaches are overcome by a method for interrupting regeneration of a particulate filter in the exhaust gas system of an internal combustion engine with the air mass flow to the engine and the intake manifold absolute pressure being detected by sensors and being varied by operating an intake throttle valve disposed in an intake duct of the engine and an EGR valve disposed in an EGR duct connected to an exhaust duct of the engine and an intake inlet duct downstream of the intake throttle valve. The method includes the steps of actuating the EGR valve to maintain a predetermined air mass flow rate and actuating the intake throttle valve to maintain a predetermined intake manifold absolute pressure. The predetermined intake manifold absolute pressure is based on a pressure correction and a desired intake manifold absolute pressure. The pressure correction depends on a difference between the predetermined mass air flow rate and a measured mass air flow rate.
DPF regeneration is generally interrupted to prevent the DPF from being destroyed by excessively high temperatures. For this reason, the method according to the invention is preferably initiated when a predetermined temperature threshold is exceeded in the DPF. However, other criteria are also feasible, in which the method can be started on other, sensible bases.
The inventors of the present invention have recognized that the variables involved in interrupting regeneration in a DPF interactively depend on each other. An advantage of the present invention is that by coordinating control of the variables, interruption of regeneration of the DPF is improved. An important aspect of the present invention is to limit the oxygen concentration of the exhaust gases at the inlet of the DPF.